Reconfigurable balancing robot and method for moving over large obstacles

ABSTRACT

An apparatus and a method for robotic control that allows an unbalanced pendulum robot to raise its Center of Mass and balance on two motorized wheels. The robot includes a pair of arms that are connected to the upper body of the robot through motorized joints. The method consists of a series of movements employing the arms of the robot to raise the robot to the upright position. The method comprises a control loop in which the motorized drives are included for dynamic balance of the robot and the control of the arm apparatus. The robot is first configured as a low Center of Mass four-wheeled vehicle, then its Center of Mass is raised using a combination of its wheels and the joint located at the attachment point of the arm apparatus and the robot body, between the rear and front wheels; the method then applies accelerations to the rear wheels to dynamically pivot and further raise the Center of Mass up and over the main drive wheels bringing the robot into a balancing pendulum configuration.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/850,842, filed on Aug. 5, 2010, which is a divisional applicationto 11/591,925, filed on Nov. 2, 2006and now issued as U.S. Pat. No.7,798,264.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The development of the invention that is the subject of the presentapplication was partially supported by Department of Defense's Office ofNaval Research and Defense Advanced Research Projects Agency.

MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to methods for control of theconfiguration and motion of a robot, without the aid of a person orother external means. More specifically, the present invention isdirected to a reconfigurable balancing combat robot and a means fordynamically transitioning from a low Center of Mass configuration to ahigh Center of Mass balancing configuration without external assistance.

2. Description of the Related Art

Robots have useful applications in many different fields. Robots areparticularly useful in combat situations, where they may be deployedinto dangerous environments without putting soldiers' lives at risk.

Various robot platforms have been developed for combat and otherapplications. Conventionally, robots utilize an on-board motor to powerwheels, tracks, or other ground-contacting devices to move the robotfrom one location to another. An operator may remotely control themovement of the robot with a joystick or other input device. Wirelesscommunication devices allow operators to be positioned a substantialdistance away from the robot.

The lack of maneuverability provided by current robot platforms hasgreatly limited the widespread use of robots in combat situations.Unlike human, soldiers, current robot platforms cannot easily maneuveraround rocks, trees, and holes. While circumventing these obstacles,robots may be easily targeted and destroyed.

Alternative robot platforms have been developed that overcome some ofthe drawbacks of a typical wheeled robot. An example of an alternativeplatform is the Goes-Over-All-Terrain (“GOAT”) robot. This platform hasfour wheels mounted on the ends of articulated arras and legs whichallow the robot to travel quickly over flat ground and maneuver over arange of obstacles higher than a wheel diameter. However, the GOAT needsat least three wheels on the ground at any time in order to maintainbalance. This limits the height that a sensor or actuator can reach andlimits the platform's maneuverability through narrow passages.

Also known in the prior art are human transporter devices that balanceon two wheels, allowing for zero turn radius and the ability to ridethrough narrow passageways. Examples of these human transporter devicesare described in U.S. Pat. No. 5,701,965 and U.S. Pat. No. 6,302,230.These transporter devices would make a poor platform for combat robots,however. The balancing vehicles described in these references lack theability to initially balance themselves when first powered on and wouldnot be able to get back up after falling down. Such a robot would alsolack a statically stable four-Wheel mode.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a robotic vehicle capable oftransitioning from a low Center of Mass (“low-COM”) configuration to ahigh Center of Mass (‘high-COM”) configuration. The robotic vehiclecomprises a rear base, a front aim, and a motorized-joint connecting therear base and the front arm. The robotic vehicle includes a rear drivemechanism attached to the rear base, and a means of locomotion using arear motorized ground-contacting module. The rear ground-contactingmodule serves to suspend the mechanism above the rear joint. A forwardground-contacting module is provided attached to the front arm. Theforward ground-contacting module may also include a brake. A controlmodule which controls the rear motorized drive is also provided. Thecontrol module includes a control loop for dynamically stabilizing thevehicle in the fore-aft plane by operation of the rear motorized drivein connection with the rear ground-contacting module. In all embodimentsthe ground-contacting modules may be skids, tracks or wheels, withoutlimitation.

In a further embodiment, the forward ground-contacting module isrealized as a motorized ground-contacting member.

In a further embodiment, the rear base is realized as a pair ofground-contacting members, laterally disposed with respect to oneanother.

In a further embodiment, the front base is realized as a pair ofground-contacting members, laterally disposed with respect to oneanother.

In a further embodiment, the front arms are realized as a pair of groundcontacting members, laterally disposed with respect to one another.

The preferred embodiment (shown in FIG. 1) has four motorized wheels forground-contacting modules. Two motorized wheels are connected to therear base and two motorized wheels are connected to the front base. Thepreferred embodiment includes independent front drive and rear drivemechanisms. The front and rear drive mechanisms may be operated in oneof several modes including: (1) a combined drive mode using the frontand rear drive mechanisms in combination when operating in the lowCenter of Mass configuration, (2) a rear-only drive mode using only therear drive mechanism when operating in the high Center of Massconfiguration, and (3) a transition mode for transitioning between thecombined drive locomotion mode and the rear drive locomotion mode.

Accordingly, the proposed reconfigurable robot has a low center of mass,statically stable mode and a high center of mass, balancing mode. Therobot can switch between modes by use of drive wheels and actuatedjoints. A control system autonomously changes between the modes and alsoprovides balance when in the balancing mode. The robot is capable oftransporting various payloads, including camera and weapon systems on aturret. The four-wheel low profile mode allows the robot to move quicklyand stably, much like a traditional wheeled vehicle. The two-wheel highprofile mode allows the robot to place its camera or weapon system at ahigh perch, thereby seeing over obstacles. This mode also allows therobot to turn with a zero turning radius. Being able to switch modesallows the robot to have a relatively narrow width. Both the narrowwidth and the zero turning-radius allow the robot to get through narrowcorridors.

According to one illustrative embodiment of the invention, there is abase, two main drive wheels attached to the base, two actuated shoulderjoints connected to the base, two arm links attached at the shoulderjoints, two wheels attached to the end of the arm links, and a controlsystem that provides a control signal to the shoulder joints and/or themain drive wheels in order to transition between a mode in which allfour wheels are in contact with the ground and a mode in which only thetwo main drive wheels are in contact with the ground.

The transition mode utilizes a transitioning process comprising thesteps of:

-   -   (a) Applying power to a combination of the rear drive mechanism,        the front drive mechanism, and the motorized joint to bring the        vehicle into a partially upright position;    -   (b) Applying power to the rear drive mechanism to accelerate the        vehicle backward;    -   (c) Applying power to the rear drive mechanism to accelerate the        vehicle forward and lift the front drive mechanism off the        ground; and    -   (d) Applying power to the rear drive mechanism in order to keep        the front drive mechanism off the ground.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the invention shown ina two-wheel high Center of Mass balance configuration.

FIG. 2 is another perspective view of the embodiment of FIG. 1, shown ina four-wheel low Center of Mass configuration.

FIG. 3 is a perspective view of the embodiment of FIG. 1 with theaddition of a camera payload mounted on an actuated turret.

FIG. 4 is a perspective view of the embodiment of FIG. 1, with theaddition of a weapon payload mounted on an actuated turret.

FIG. 5 is a perspective view of another embodiment of the inventionshown in a to Center of Mass Configuration (a) and a high Center of MassConfiguration (b).

FIG. 6 is a perspective view of another embodiment of the inventionshown in a low Center of Mass Configuration (a) and a high Center ofMass Configuration (b).

FIG. 7 shows a flowchart detailing an algorithm for transitioning thedevice from a low Center of Mass configuration to a high Center of Massbalance configuration.

FIG. 8 shows a flowchart detailing an algorithm for transitioning thedevice from a high Center of Mass balance configuration to a low Centerof Mass configuration.

FIG. 9 is a time-lapsed image sequence of the embodiment of FIG. 4transitioning from a four-wheel low Center of Mass configuration to afour-wheeled A-frame configuration to a two wheeled high Center of Massbalance configuration.

FIG. 10 shows a time-lapsed composite image of one embodiment of theinvention transitioning from a four-wheel low Center of Massconfiguration to a four-wheeled A-frame configuration.

FIG. 11 shows a time-lapsed composite image of one embodiment of theinvention transitioning from a four-wheeled A-frame configuration to atwo-wheeled high Center of Mass balance configuration.

FIG. 12 shows a time-lapsed image sequence of the embodiment of FIG. 4driving over a relatively small obstacle.

FIG. 13 shows a time-lapsed image sequence of the embodiment of FIG. 4driving over a relatively large obstacle.

FIG. 14 shows a model on an inverted pendulum on a wheel. This model isuseful for analyzing and designing the balance controller for the robot

FIG. 15 shows a model of one embodiment of the invention useful forcomputing the wheel and shoulder joint torques in order to transitionfrom a low Center of Mass configuration to an A-frame configuration.

FIG. 16 shows a model of one embodiment of the invention useful forcomputing a sequence of actions for dynamically transitioning from anA-frame configuration to a high Center of Mass balance configuration.

FIG. 17 shows a model of one embodiment of the invention with a gunturret carriage useful for computing a sequence of actions forcontrolling the pitch of the gun mount while transitioning from a LowCenter of Mass configuration to a high Center of Mass configuration.

FIG. 18 shows a control system diagram.

FIG. 19 shows an exploded view of the embodiment of FIG. 4.

REFERENCE NUMERALS IN THE DRAWINGS

-   20 Base-   30 main drive wheel-   31 main drive wheel-   32 motor amplifier-   34 electric motor-   36 gear reduction-   40 powered shoulder joint-   41 powered shoulder joint-   50 arm link-   51 arm link-   60 wheel-   61 wheel-   70 suspension system-   80 track system-   90 turret-   92 embedded computer system-   94 inertial measurement unit-   100 weapon system-   110 camera system-   200 rear ground contacting member-   205 rear drive wheel-   206 rear track-   210 rear base-   220 powered joint-   230 front base-   240 front ground contacting member-   245 front drive wheel-   246 front track-   700 obstacle-   1600 embedded processor-   1601 embedded processor batteries-   1602 pitch, roll, and yaw sensors-   1603 motor drive batteries-   1610 left arm wheel rotation sensor-   1611 left arm wheel motor-   1612 left arm wheel amplifier-   1615 right arm wheel, rotation sensor-   1616 right arm wheel amplifier-   1617 right arm wheel motor-   1620 GPS device-   1630 compass-   1640 wireless high speed data link-   1650 left shoulder rotation sensor-   1651 left shoulder motor-   1652 left shoulder amplifier-   1655 right shoulder rotation sensor-   1656 right shoulder amplifier-   1657 right shoulder motor-   1660 left rear wheel rotation sensor-   1661 left rear wheel motor-   1662 left rear wheel amplifier-   1665 right rear wheel rotation sensor-   1666 right rear wheel amplifier-   1667 right rear wheel motor-   7000 Stand-Up command-   7100 watchdog timer-   7110 step-   7120 step-   7130 step-   7140 comparator-   7150 comparator-   7160 fault code-   7200 watchdog timer-   7210 step-   7220 comparator-   7230 comparator-   7240 fault code-   7300 watchdog timer-   7310 step-   7320 comparator-   7330 comparator-   7340 fault code-   7400 balancing mode-   8000 Lie-Down command-   8100 watchdog timer-   8110 step-   8120 comparator-   8130 comparator-   8140 fault code-   8200 watchdog timer-   8210 step-   8220 comparator-   8230 comparator-   8240 fault code-   8300 watchdog tinier-   8310 step-   8320 step-   8330 comparator-   8340 comparator-   8350 fault code-   8400 four-wheel ground contact stasis-   9020 solenoid-activated gear-   9030 gun mount carriage-   9040 gears

DETAILED DESCRIPTION OF THE INVENTION

The invention may be implemented in a wide range of embodiments. Acharacteristic of many of these embodiments is the ability to transitionfrom a low Center of Mass configuration to a high Center of Massbalancing configuration. In the low Center of Mass configuration, a setof rear ground contacting members and a set of front ground contactingmembers provide a stable base of support in the high Center of Massconfiguration, only one set of ground contacting members (typically therear ground contacting members) provide ground support while the otherset (typically the front ground contacting members) are raised off theground. An actuated joint located between the rear ground contactingmembers and the front ground contacting members is used to raise theCenter of Mass when transitioning between the low Center of Massconfiguration and the high Center of Mass configuration, and also tohold up the front ground contacting members when in the high Center ofMass configuration. A transitioning process is provided, for transitionto the high Center of Mass configuration.

FIGS. 1 and 2 show perspective views of one embodiment of the invention.Two main drive wheels 30, 31 are connected to base 20. Main drive wheels30, 31 can each he powered by various means, including an electric motorwith a gear reduction, a hydraulic motor, or an internal combustionengine and transmission. Suspension system 70 may also provide supportbetween base 20 and main drive wheels 30, 31. Two powered shoulderjoints 40, 41 are connected to the base. The shoulder joints also may bepowered by various means, including electric motors with gearreductions, hydraulic motors, or internal combustion engines. Two armlinks 50, 51 are connected to the shoulder joints. Two arm wheels 60, 61are connected at the end of the arm links. These wheels may be eitherpassive or powered and may or may not have a steering mechanism.

FIG. 1 shows the invention in an upright two-wheeled high Center of Massbalance configuration in which a control system provides a command tomain drive wheels 30, 31 in order to balance the robot on the two maindrive wheels. The reader will note that when the robot is in the balanceconfiguration, the front wheels are off the ground. Accordingly, thecontrol system sends control signals to the motors that power the rearwheels. The control signal sent by the control system is related to ameasurement of the robot's Center of Mass with respect to the contactpoint of the wheels that are contacting the ground. Such a measurementcould come from a gyroscope mounted in the base, an inertial measurementunit mounted in the base, a camera system mounted to the base or arms,or other means.

FIG. 2 shows the invention in a four-wheel low Center of Massconfiguration. In this configuration powered shoulder joints 40, 41 canbe locked in order to maintain the configuration, or they can be used inconjunction with main drive wheels 30, 31 and arm wheels 60, 61 in orderto raise or lower the Center of Mass. The powered shoulder jointsaccomplish this by supplying a torque between the base and each of thearms.

FIG. 3 shows a perspective view of the embodiment of FIG. 1 and FIG. 2with the addition of a camera system and trade system. In thisembodiment, track system 80 is attached to base 20. Turret 90 is alsoattached to base 20, and camera system 110 is attached to turret 90.Camera system 100 may be remotely controlled and oriented through thecontrol of turret 90. Track system 80 can be used in order to get overrough terrain. One or more drive wheels may be powered to drive the beltor “track.” Track system 80 may operate similarly to caterpillar-type orKegresse-type track systems. That is the track may comprise interlockingmetal segments or a flexible material.

FIG. 4 shows a perspective view of the embodiment of FIG. 1 and FIG. 2with the addition of a weapon system. In this embodiment, track system80 is attached to base 20. Turret 90 is also attached to the base 20,and weapon system 100 is attached to turret 90. In this embodiment theweapon system 100 may be remotely controlled and oriented through thecontrol of turret 90.

FIGS. 5(a) and 5(b) show a simplified embodiment of the invention in alow Center of Mass configuration and a high Center of Massconfiguration, respectively. Rear drive wheel 205 is connected to rearbase 210. Rear drive wheel 205 can be powered by various means,including electric or hydraulic motors. Powered joint 220 is connectedto rear base 210. Powered joint 220 may also be powered by variousmeans, including electric or hydraulic motors. Front base 230 isconnected to powered joint 220. Front drive wheel 245 is connected tofront, base 230. The front wheel may be either passive or powered andmay or may not have a steering mechanism.

FIGS. 6(a) and 6(b) show another embodiment of the invention in a lowCenter of Mass configuration and a high Center of Mass configuration,respectively. Rear ground contacting member 200 includes one or morerear tracks 206 connected to rear base 210. Rear tracks 206 can bepowered by various means, including electric or hydraulic motors.Powered joint 220 is connected to rear base 210. Powered joint 220 mayalso be powered by various means, including electric or hydraulicmotors. Front base 230 is connected to powered joint 220. Front groundcontacting member 240 includes one or more front tracks 246 connected tofront base 230. Front tracks 246 can be powered by various means,including electric or hydraulic motors.

FIG. 7 shows a flowchart detailing a process for transitioning from alow Center of Mass configuration to a high Center of Mass balanceconfiguration. When Stand-Up command 7000 is received, watchdog timer7100 is loaded with the expected time required for the operation. Torqueis then applied in the forward direction, as indicated by step 7110, tothe drive(s) of the rear ground-contacting member concurrently with theapplication of torque in the reverse direction to the drive(s) of thefront ground-contacting member as indicated by step 7120. Lifting torqueis also applied to the drive(s) of the arm attachment joint concurrentlywith the application of torque to the ground-contacting members asindicated by step 7130.

Comparator 7140 determines whether the robot has attained the thresholdangle (60 degrees in the present example). Comparator 7140 makes thisdetermination by comparing input data provided by a sensor to thepredefined threshold angle. If the robot has not attained the thresholdangle comparator 7140 looks to comparator 7150 to determine if the timerof watchdog timer 7190 has expired. If watchdog timer 7109 has expired,fault code 7160 is generated. The process may then be repeated.

When the pitch of the robot has ascended to an angle greater than adesired maximum, placing the robot in an A-frame pose, a reverse torqueis applied to the rear ground-contacting members as indicated by step7210. This reverse torque accelerates the robot backward until asufficient speed in the reverse direction is reached. Watchdog timer7200 is loaded with the time expected to attain sufficient speedconcurrently with the application of reverse torque. Comparator 7220determines Whether the speed of the robot has attained the thresholdspeed required. If the threshold speed has not been attained comparator7220 looks to comparator 7230 to determine whether watchdog timer 7200has expired, if watchdog timer 7200 has expired, fault code 7240 isgenerated. The process may then be repeated from Stand-Up command 7000.

If a sufficient speed is attained, the torque on the rear drives ischanged to accelerate the robot in the forward direction as indicated bystep 7310, dynamically lifting the aspect of the robot further to thevertical. Watchdog timer 7310 is also loaded concurrently with theapplication of the forward torque. Watchdog tinier 7310 is loaded withthe expected time required to attain a vertical pose once a sufficientforward speed has been attained, Comparator 7320 is used to determinewhether the vehicle has attained a pitch greater than 90 degrees. If avertical pose has not been attained, comparator 7320 looks to comparator7330 to determine if watchdog tinier 7310 has expired. If watchdog timer7310 has expired, fault code 7340 is generated. The process may then berepeated from Stand-Up command 7000.

When a vertical pose is attained, the control switches to balancing mode7400 and the robot is brought into balancing stasis.

FIG. 8 shows a flowchart detailing a process for transitioning from ahigh. Center of Mass balance configuration to a low Center of Massconfiguration. When Lie-Down command 8000 is received, watchdog timer8100 is loaded with the expected time required for the operation.Backward torque is concurrently applied to the motorized drives of therear ground-contacting member, as indicated by step 8110. This causesthe robot to begin to tilt forward. Comparator 8120 determines whetherthe vehicle has attained a threshold pitch (less than 85 degreesmeasured from the horizontal in the present example). If the vehicle hasnot attained the threshold pitch, comparator 8120 look to comparator8130 to determine whether watchdog timer 8100 has expired. If watchdogtimer 8100 has expired, fault code 8140 is generated. The process maythen be repeated.

When sufficient reduction in pitch is attained, the torque is removedfrom the rear ground-contacting member and the robot is allowed tosettle into the A-Frame position as indicated by step 8210. Watchdogtimer 8200 is concurrently loaded with the time expected to complete theoperation. Comparator 8220 determines whether the front base of thevehicle has made contact with the ground. If it has not, comparator 8220looks to comparator 8230 to determine whether watchdog timer 8200 hasexpired. If watchdog timer 8200 has expired, fault code 8240 isgenerated. The process may then be repeated from Lie-Down command 8000.

When contact of the front ground-contacting member and the ground isconfirmed by comparator 8220, a reverse torque is applied to themotorized drives of the rear ground contacting member as indicated bystep 8310. Forward torque is concurrently applied to the motorizeddrives of the forward wound-contacting member as indicated by 8320 untilthe aspect of the robot is brought down to a desired threshold angle.Watchdog timer 8300 is loaded with the expected time to reach thethreshold angle. Comparator 8330 determines whether the vehicle hasattained the threshold angle (less than 10 degrees in the presentexample). If the threshold angle has not been attained, comparator 8330looks to comparator 8340 to determine whether watchdog timer 8300 hasexpired. If it has, fault code 8350 is generated. The process may thenbe repeated from Lie-Down command 8000. Once the vehicle attains thethreshold angle, the torques are removed, leaving the robot infour-wheel ground contact stasis 8400.

FIG. 9 is a time-lapsed image sequence of the embodiment shown in FIG. 4transitioning from a four-wheel to Center of Mass configuration (a) to afour-wheeled A-frame configuration (d) to a two-wheeled high Center ofMass balance configuration (l). In this image sequence, a combination ofmain drive wheels 30, 31, arm wheels 60, 61, and shoulder joints 40, 41are used to raise the Center of Mass.

FIG. 10 shows a time-lapsed composite image of a simplified embodimentof the invention transitioning from low Center of Mass configuration toan A-frame configuration. Rear ground contacting member 200 is attachedto rear base 210. The rear base is connected to powered joint 220. Thepowered joint is connected to front base 230. The front base isconnected to front ground contacting member 240. When in both the lowCenter of Mass configuration and in the A-frame configuration, both therear ground contacting member and the front ground contacting member arein contact with the ground. During the transition from the low Center ofMass configuration to the A-frame configuration, power is applied to acombination of the rear ground contacting member 200, powered joint 220,and front ground contacting member 240. One such method of applyingpower to a specific embodiment of the invention is describedsubsequently.

FIG. 11 shows a time-lapsed composite image of one embodiment of theinvention transitioning from an A-frame configuration to a high Centerof Mass balance configuration. Rear ground contacting member 200 isattached to rear base 210. The rear base is connected to powered joint220. The powered joint is connected to front base 230. The front base isconnected to front ground contacting member 240. When in the A-frameconfiguration, both the rear ground contacting member and the frontground contacting member are in contact with the ground. When in thehigh Center of Mass balance configuration, the rear ground contactingmember is in contact with the ground, while the front ground contactingmember is not in contact with the wound. During the transition from theA-frame configuration to the high Center of Mass balance configuration,power is applied to rear wound contacting member 200 to raise the Centerof Mass up and over rear wound contacting member 200. One such method ofapplying power to a specific embodiment of the invention is describedsubsequently,

FIG. 12 shows a time-lapsed image sequence of the embodiment of theinvention shown in FIG. 4 riding over a relatively small obstacle inthis image sequence, the robot slows down on the approach of theobstacle (a); drives toward the obstacle, initiating contact between theobstacle and the rear drive wheel (b); applies a torque to the reardrive wheel to lift its center of mass onto the obstacle while balancing(c); drives over the obstacle (d); drives off the obstacle (e); anddrives away from the obstacle (f). Throughout this motion, the robotremains balanced using a balance control method Which is described ingreater detail subsequently.

FIG. 13 Shows a time-lapsed image sequence of the embodiment of theinvention shown in FIG. 4 riding over a relatively large obstacle. Inthis image sequence, the robot lifts its arm links 50, 51 and arm wheels60, 61 while approaching obstacle 700 while balancing (a); lowers itsarm wheels 60, 61 onto the obstacle and lowers its base 20 such thattrack system 80 on base 20 makes contact with obstacle 700 (b); usestrack system 80 to pull itself up and onto obstacle 700 (c); makescontact between main drive wheels 30, 31 and the top of obstacle 700 anduses a combination of track system 80 and main drive wheels 30, 31 todrive over obstacle 700, while arm wheels 60, 61 regain contact with theground (d); finishes driving over obstacle 700 using main drive wheels30, 31 (e); loses contact between main drive wheels 30, 31 and obstacle700 and regains contact between main drive wheels 30, 31 and the ground(f). During this maneuver, turret 90 can be operated to orient weaponsystem 100 to a desired orientation with respect to the ground,independent of the configuration of the robot. Track system 80 may beremotely actuated by an operator or it may be automatically actuatedwhen the robot detects that its forward progress is impeded by theobstacle.

FIG. 14 shows a mathematical model of an inverted pendulum on a wheel.This model is useful for analyzing and designing the balance controllerfor the balance configuration, as described subsequently.

FIG. 15 shows a mathematical model of one embodiment of the inventionuseful for computing the wheel and shoulder joint torques in order totransition from a low Center of Mass configuration to an A-frameconfiguration, Rear drive wheel 205 is connected to rear base 210. Rearbase 210 is connected to powered joint 220. Front base 230 is alsoconnected to powered joint 220. Front drive wheel 245 is connected tofront base 230. In this model, the following assumptions are made: (1)the Center of Mass of the device lies at the location of powered joint220; (2) the entire device has a mass of M; (3) front base 230 and rearbase 210 are both of the same length, L; (4) wheels 205, 245 are both ofthe same radius, R; (5) the torque applied to the powered joint 220 isτ_(S); (6) the torque applied to each wheel 205, 245 is τ_(W); and (7)the center of mass is at a vertical height, h, above the center of thewheels, and at a horizontal distance, w, from the center of the wheels.

Shown in FIG. 15 are various symbols representing the forces and torqueson the system. F_(X) is the horizontal force between the pound and eachwheel, and also between each wheel and its associated base. F_(Z) is thevertical force between the ground and each wheel, and also between eachwheel and its associated base. Mg is the force produced by gravitationon the mass. With this model, the relation between the quantitiesrequired to support the mass is

${\tau_{S} + {\frac{\left( {h + R} \right)}{R}\tau_{W}}} = {\frac{1}{2}{Mgw}}$

The derivation of this equation is explained subsequently. This relationcan be used to compute the torque at wheels 205, 24 and powered joint220 needed to support the mass. If larger torques are applied, then themass will accelerate upward, raising the Center of Mass. If smallertorques are applied, then the mass will accelerate downward, loweringthe Center of Mass.

Balancing in the High Center of Mass Configuration

The reconfigurable robot balances when in the high Center of Massconfiguration. Control action required to balance this configuration isgenerally accomplished by: (1) computing the dynamic equations of motionfor the robot; (2) linearizing the dynamic equations; (3) determining aparameterized feedback control system; and (4) determining suitableand/or optimal control system parameters using one of a number ofdifferent mathematical control system tools.

As a first approximation to the full dynamics of the reconfigurablerobot, we can compute the equations of motion of a simplified systemconsisting of an inverted pendulum on a single wheel, as shown in FIG.14 This system is a simplification of a balancing robot, taking intoaccount only planar motion and locked aims. The equations of motion canbe determined using either a free-body diagram approach or a Lagrangianapproach. Both approaches result in the following equations of motion:

$\begin{bmatrix}{M_{W} + M_{P} + \frac{J_{W}}{R_{W}}} & {M_{P}L_{P}\cos\;\theta_{P}} \\{M_{P}L_{P}\cos\;\theta_{P}} & {J_{P} + {M_{P}L_{P}^{2}}}\end{bmatrix}{\quad{{\begin{bmatrix}{\overset{¨}{X}}_{W} \\{\overset{¨}{\theta}}_{P}\end{bmatrix} + \begin{bmatrix}{{- M_{P}}L_{P}\sin\;\theta_{P}{\overset{.}{\theta}}_{P}^{2}} \\0\end{bmatrix} + \begin{bmatrix}0 \\{{- M_{P}}L_{P}g\;\sin\;\theta_{P}}\end{bmatrix}} = {\begin{bmatrix}\frac{1}{R_{W}} \\{- 1}\end{bmatrix}\tau}}}$where X_(W) is the forward position of the center of the wheels andθ_(P) is the angle of the platform with respect to vertical, M_(P) isthe mass of the upper body platform and arms, L_(P) is the distance fromthe wheel pivot to the Center of Mass of the platform, J_(P) is themoment of inertia of the pendulum about its Center of Mass, M_(W) is thetotal mass of the main drive wheels, J_(W) the moment of inertia of themain drive wheels about their Center of Mass, R_(W) is the radius of amain drive wheel, τ is the torque applied, and g is the gravitationalacceleration constant. The various length, mass, and inertia propertiescan be estimated from CAD models, measured through various experimentaltechniques, or estimated online during operation of the robot usingstandard adaptive control techniques.

The equations of motion can be linearized about the upright balancingconfiguration and solved in terms of the state variables:

$\begin{bmatrix}{\overset{¨}{X}}_{W} \\{\overset{¨}{\theta}}_{P}\end{bmatrix} + {\begin{bmatrix}0 & M_{12} \\0 & M_{22}\end{bmatrix}\begin{bmatrix}X_{W} \\\theta_{P}\end{bmatrix}} + {\begin{bmatrix}B_{1} \\B_{2}\end{bmatrix}\tau}$The four condensed parameters of these equations of motion are:

${M_{12} = \frac{{- M_{P}^{2}}L_{P}^{2}g}{den}};$${M_{22} = \frac{M_{P}L_{P}{g\left( {M_{W} + M_{P} + \frac{J_{W}}{R_{W}^{2}}} \right)}}{den}};$${B_{1} = \frac{{M_{P}L_{P}} + \frac{J_{P}}{R_{W}} + \frac{M_{P}L_{P}^{2}}{R_{W}}}{den}};{and}$${B_{2} = \frac{M_{W} + M_{P} + \frac{J_{W}}{R_{W}^{2}} + \frac{M_{P}L_{P}^{2}}{R_{W}}}{den}},$where den=(M_(W)+M_(P))J_(P)+M_(W)M_(P)L_(P) ²+J_(W)/R_(W)²(J_(P)M_(P)L_(P) ²).

A simple linear control law that can balance the system isτ=K ₁(X _(W) _(des) −X _(W))+K ₂({dot over (X)} _(W) _(des) −{dot over(X)} _(W))+K ₃(θ_(P) _(des) −θ_(P))+K ₄({dot over (θ)}_(P) _(des) −{dotover (θ)}_(P))

Using this control law and rewriting the resultant linearized equationsof motion in the form {dot over (X)}=AX+Bu, where X is the statevariables and u are the inputs, we get

${\frac{\mathbb{d}}{\mathbb{d}t}\begin{bmatrix}X_{W} \\{\overset{.}{X}}_{W} \\\theta_{P} \\{\overset{.}{\theta}}_{P}\end{bmatrix}} = {\begin{bmatrix}0 & 1 & 0 & 0 \\{{- B_{1}}K_{1}} & {{- B_{1}}K_{2}} & {M_{12} - {B_{1}K_{3}}} & {{- B_{1}}K_{4}} \\0 & 0 & 0 & 1 \\{{- B_{2}}K_{1}} & {{- B_{2}}K_{2}} & {M_{22} - {B_{2}K_{3}}} & {{- B_{2}}K_{4}}\end{bmatrix}{\quad{\begin{bmatrix}X_{W} \\{\overset{.}{X}}_{W} \\\theta_{P} \\{\overset{.}{\theta}}_{P}\end{bmatrix} + {\begin{bmatrix}0 & 0 & 0 & 0 \\{B_{1}K_{1}} & {B_{1}K_{2}} & {B_{1}K_{3}} & {B_{1}K_{4}} \\0 & 0 & 0 & 0 \\{B_{2}K_{1}} & {B_{2}K_{2}} & {B_{2}K_{3}} & {B_{2}K_{4}}\end{bmatrix}\begin{bmatrix}X_{W_{des}} \\{\overset{.}{X}}_{W_{des}} \\\theta_{P_{des}} \\{\overset{.}{\theta}}_{P_{des}}\end{bmatrix}}}}}$

The eigenvalues of the A matrix will determine the stability and theresponse time of the system and will depend on the feedback parameters,K₁ through K₄. These parameters can be chosen in many ways, includingpole placement, LQR techniques, and simply trial and error.

This technique gives a combined applied torque of τ. This torque can beapplied to typical embodiments of the invention by dividing it among themain drive mechanisms. For example, in the embodiment of FIG. 1, halfthe torque can be applied to main drive wheel 30, and half the torquecan be applied to main drive wheel 31.

Turning in the High Center of Mass Configuration

In a typical embodiment of the invention, such as the embodiment shownin FIGS. 1 and 2, the robot can turn about a vertical axis bydifferentially driving main drive wheels 30, 31. The following controllaw can he used to determine the differential torque to apply to thewheels,τ_(Y) =K ₅(θ_(Y) _(des) −θ_(Y))+K ₆({dot over (θ)}_(Y) _(des) −{dot over(θ)}_(Y))where τ_(Y) is the differential torque to apply to the main drive wheels30, 31; θ_(Y) _(des) is the desired yaw angle (rotation about thevertical axis); θ_(Y) is the measured yaw angle; {dot over (θ)}_(Y)_(des) the desired yaw velocity; {dot over (θ)}_(Y) is the measured yawvelocity; and K₅ and K₆ are control gains. The desired yaw and yawvelocity may come from a user input interface or from a higher-levelcontroller. The measured yaw and yaw velocity may come from a gyroscope,inertial measurement unit, vision system, or other sensing means. Thecontrol gains, K₅ and K₆ can be chosen using a variety of methods knownto those familiar with control system design.

This technique gives a differential applied torque of τ_(Y). This torquecan be applied to typical embodiments of the invention by distributingit among the main drive mechanisms. For example, in the embodiment ofFIG. 1, half the torque can be applied to main drive wheel 30, and anequal and opposite torque can be applied to main drive wheel 31. Thiswill provide a differential torque that results in the control of yawand yaw velocity. The reader will note that both the control of balanceand the control of turning can be achieved simultaneously by applyingthe above techniques simultaneously through the summation of theresultant torques at each wheel.

Transitioning Between Modes

Various embodiments of the invention transition between severalgeometric configurations and their associated modes of operation,including a two-wheeled balancing configuration, a four-wheeled lowCenter of Mass configuration, and a four-wheeled A-frame configuration.Switching between the configurations can be initiated by a humanoperator When the robot is being teleoperated or automatically duringautonomous or semi-autonomous operation.

When in the four-wheeled low Center of Mass configuration, the robot hasa low profile and operates much like a remote-controlled car, orconventional four-wheeled robot. Steering and Velocity commands can bedirectly interpreted into wheel velocity commands.

To transition from the four wheel low Center of Mass configuration tothe four-wheeled A-frame configuration, the front wheels can becommanded to drive backwards and the rear wheels can be commanded todrive forward, while the shoulder motors are commanded to be driven tomake the robot form an A shape. Once in the A-frame configuration, ifdesirable, brakes on the shoulder motors can be applied to lock theshoulders, reducing the power consumption at those joints. FIG. 15 showsa schematic of a specific embodiment of the invention that can be usedto compute the wheel and shoulder motor torques that can be applied totransition from a low Center of Mass configuration to an A-frameconfiguration. Performing force balance on the wheel, we haveF _(x)=τ_(W) /RPerforming a force balance in the vertical axis, we haveF _(Z) =Mg/2Performing a torque balance about the mass, we have2F _(Z) w−2F _(X) h−2τ_(W)=2τ_(S)Solving the above equations to eliminate F_(x) and F_(Z) we get,

${\tau_{S} + {\frac{\left( {h + R} \right)}{R}\tau_{W}}} = {\frac{1}{2}{Mgw}}$

We see that the Center of Mass can be lifted through multiplecombinations of shoulder torque or wheel torques. For example, if onlyshoulder torque is provided, we get

$\tau_{S} = {\frac{1}{2}{Mgw}}$whereas if only wheel torque is provided, we get

$\tau_{W} = {\frac{R}{2\left( {h + R} \right)}{Mgw}}$

The reader will note that the front and rear wheels do not bothnecessarily need to be motorized in order to provide a wheel torqueτ_(W). For example, the front wheels could have a brake instead of amotor and be locked in place. τ_(W) could then be applied to just therear wheel, producing nearly the same effect as had the wheel torquebeen applied to both wheels. The only difference would be that insteadof the Center of Mass transitioning straight vertically, the front wheelwould stay in its position on the ground and the Center of Mass wouldtransition both horizontally and vertically. The above equations are forthe model in which the Center of Mass lies directly at the poweredjoint, the front and rear base lengths are the same, the wheel diametersare the same, and the wheel torques are the same. This model was chosenfor simplicity of demonstration to demonstrate one specific embodimentof the invention. One skilled. In the art should be able to easilycompute related equations for other embodiments of the invention.

Dynamic Transition to the Balancing Configuration

A robot dynamically transitioning to the balancing configuration isillustrated in FIG. 16. During transition from the low Center of Massconfiguration to the high Center of Mass configuration, the robot passesthrough a sequence of configurations in which the projection of theCenter of Mass of the robot onto the ground (the Ground Projection ofthe Center of Mass) lies outside the Ground Support Polygon of therobot. The Center of Mass is the weighted average location of all of themass of the robot. The Ground Projection of the Center of Mass, P_(com),is the point on the ground directly below the Center of Mass location.The Ground Support Polygon is defined by the convex hull of all thepoints of contact between the robot and the ground. Both “GroundProjection of the Center of Mass” and “Ground Support Polygon” are tomscommonly used in dynamically balanced robotic fields, for example thefield of legged robots. “Convex hull” is a term commonly used inmathematics. The convex hull of a set of points, X, is the minimalconvex set containing X. If all ground contacting points lie in the sameplane, the convex hull may be visualized by imagining an elastic bandstretched to encompass gall of the ground contacting points. If aperpendicular stake (perpendicular relative to the plane) is placed atthe location of each ground contacting point, the elastic band will takeon the shape of the convex hull when the elastic baud is released,

A robot with Static Mobility is one in which the Ground Projection ofthe Center of Mass always lies within the Ground Support Polygon. Oneexample would be a slow walking hexapedal robot with an alternatingtripod gait. A robot with Dynamic Mobility is one in which, the GroundProjection of the Center of Mass occasionally lies outside the GroundSupport Polygon. One example would be a fast walking or running biped. Arobot with Static Mobility can move at slow speeds without considerationfor the dynamics of the robot, but only with consideration for thegeometric kinematics of the robot. A robot with Dynamic Mobility mustmove in such a way that takes dynamics into consideration. For example,a bipedal walking robot cannot come to a stop at an arbitrary point inits gait. When the (hound Projection of the Center of Mass lies outsidethe Ground Support Polygon, the robot must continue moving and take astep or it will fall down.

The main advantage of Static Mobility is that when the Ground Projectionof the Center of Mass is inside the Ground Support Polygon, the robot istypically very stable and resistant to disturbances or tipping. A mainadvantage of Dynamic Mobility is high maneuverability since it is not arequirement that the Ground Projection of the Center of Mass staysinside the Ground Support Polygon. The present invention can transitionbetween Static Mobility configurations and Dynamic Stabilityconfigurations. Depending on the situation, a configuration can bechosen based on the importance of the advantages of that configuration.

Many embodiments of the present invention exhibit Dynamic Mobility whendynamically transitioning from a low Center of Mass configuration to ahigh Center of Mass configuration. In the following discussion, theembodiments of FIG. 4 and FIG. 9 are considered, although the discussionpertains to any embodiment of the present invention that exhibitsdynamic mobility.

To dynamically transition from the low Center of Mass configuration tothe high Center of Mass two-wheeled balancing configuration, the robotprovides a rotational torque with rear drive wheels 30, 31. There are anumber of ways to provide this torque. In one way, the robot starts froma stationary position and applies a large torque to the rear wheels,thereby lifting the front wheels, much like a motorcycle “popping awheelie”. However, using this technique requires a large forwarddisplacement of the robot as the wheel torque that lifts the body of therobot also produces a large forward acceleration of the robot. Theamount of forward displacement required is in relation to the amount ofrear drive wheel torque that is applied. The larger the rear drive wheeltorque, the less displacement required. Thus it is preferable to applythe maximum available torque. However, drive components such as electricmotors have maximum torque limits and with typical components availabletoday, a significant forward displacement occurs using this method.

A preferred method is to first apply a reversing torque to the reardrive wheels when in the A-frame configuration (FIG. 9e,f ), therebycausing a backward velocity of the robot. Then, after a period of timehas passed or the robot has achieved a predefined threshold backwardvelocity, a large forward torque is applied to the rear wheels. Thisforward torque both stops the backward translational velocity of therobot and also lifts the body of the robot (FIG. 9(g), (h), (i)). Aftera predefined period of time, or after a threshold pitch is reached, thebalancing control system is then switched on and the robot balances(FIG. 9(j), (k), (l)). A flowchart illustrating an implementation ofthis method is provided in FIG. 7 (and described previously).

This method of first providing a backward velocity before applying aforward rear drive wheel torque is preferred because a minimal amount ofbody displacement is produced as a result of the transition. Both insimulation studies and prototype experimentation, it has been determinedthat a robot can perform this dynamic transition in less than one meterof total travel. Determining the amount of torque to apply and theconditions for transitioning from reverse torque to forward torque canbe achieved in a number of ways, including manual tuning of parameters,automatic tuning through adaptive control and learning controltechniques, and automatic tuning through parameter search methods suchas gradient descent and genetic algorithms.

The reader should note that this method can work whether the robotstarts in a low Center of Mass configuration (FIG. 9a ) or anintermediate Center of Mass A-Frame Configuration (FIG. 9d ). However,starting in the A-Frame configuration is preferable, as the amount ofrear drive wheel torque required to perform the maneuver is reduced, andthe amount of travel required to perform the maneuver is reduced.

The reader will note that in FIG. 16, the Ground Projection of theCenter of Mass falls a substantial distance, ΔX, away from the supportpoints of the wheels. When ΔX is large, as in FIG. 16, the robotdynamically transitions to the balance configuration. In order to do so,a corresponding large torque will be applied to the main wheels. Lesstorque is required when ΔX is small. As mentioned previously, the methodof hacking up and then accelerating forward may also be used to reducethe forward distance of travel required to transition to the balancingconfiguration.

Leveling the Turret During Transitions

It is a further object of the present invention to provide a method forrotating a gun carriage into a level position during the transitions tothe several operating positions previously described. The amount ofpitch movement is not always available within the mounted gun turretassembly, so an additional mechanism known as a gun mount carriageassembly is incorporated.

As illustrated in FIG. 17, the rate R ({dot over (α)}) that gun mountcarriage 9030 needs to rotate to keep the gun mount carriage level whenthe robot is balanced is about 0.8 times the rate of rotation of arm 50.This is derived from the fact that the arms will rotate through an angleof θ to the A-frame position while the gun mount carriage needs to moveonly θ/2 deg. The mount needs an additional α deg of forward rotation tobe level when the balanced position is attained and the total rotationof the carriage is φ=θ/2+α. This determines the gear reduction or rateto be R=φ/θ or 0.5+α/θ. A solenoid-activated gear 9020 with this ratiois attached between gears on arm motor shafts 40 and corresponding gears9040 on the gun mount carriage. The carriage rotation is capable ofbeing locked at the three cardinal positions (cart, A-frame andbalanced) using beveled solenoid operated pins. With this configurationthe gun mount carriage will rotate slightly ahead of the angularposition of the arms at a rate of R times the moving angle of the turn.However, during the movement to A-frame this rate needs to be only halfof the arm rate to keep the gun level so the extra rate, α/θ, isautomatically removed by the gun leveling feature of the turret. Whenthe robot reaches the A-frame position the gun carriage is locked, thearms gear disengaged, and α-degrees of turret elevation have beenconsumed. As the robot is configured farther into the balancing posture,the gun turret-leveling feature keeps the gun level, removing the extraα-degrees of pitch from the turret elevation. Once balanced theavailable pitch range of the gun will he the full elevation range of theturret.

A control system for the control of the robot is illustrated in FIG. 18.Embedded processor 1600 receives input signals from wireless high speeddata link 1640. Wireless high speed data link 1640 provides directionalcontrol over the operation of the robot. In particular, wireless datalink 1640 directs the robot to move forward and backward, to turn leftand right, to switch between low center of mass and high center of massoperating modes, and to control the weapons or camera systems. Embeddedprocessor 1600 also receives inputs from various sensors includingpitch, roll, and yaw sensors 1602 which provide orientation feedback toembedded processor 1600. This orientation feedback is particularlyuseful in holding the robot in the balancing configuration as discussedpreviously. Embedded processor 1600 also receives input from GPS device1620 and compass 1630. Embedded processor batteries 1601 provides powerfor controlling the various operations carried out by embedded processor1600.

Embedded processor 1600 directs torque to left rear wheel motor 1661 andright rear wheel motor 1667 through left rear wheel amplifier 1662 andright rear wheel amplifier 1666, respectively. Embedded processor 1600receives data regarding the rate of rotation of the left rear wheel andthe right rear wheel via left rear wheel rotation sensor 1660 and rightrear wheel rotation sensor 1665, respectively.

Embedded processor 1600 directs torque to left shoulder motor 1651 andright shoulder motor 1657 through left shoulder amplifier 1652 and rightshoulder amplifier 1656, respectively. Embedded processor 1600 receivesdata regarding the rate of rotation of the left shoulder and rightshoulder via left shoulder rotation sensor 1650 and right shoulderrotation sensor 1655, respectively.

Embedded processor 1600 directs torque to left arm wheel motor 1611 andright arm wheel motor 1617 through left arm wheel amplifier 1612 andright arm wheel amplifier 1616, respectively. Embedded processor 1600receives data regarding the rate of rotation of the left arm wheel andthe right arm wheel via left arm wheel rotation sensor 1610 and rightarm wheel rotation sensor 1615, respectively. Power is supplied to theaforementioned amplifiers through motor drive batteries 1603.

An exploded view of the present invention is provided in FIG. 19.Inertial measurement unit 94 is attached to base 20. Inertialmeasurement unit 94 includes sensors capable of detecting pitch, roll,and yaw of base 20. Inertial measurement unit 94 may optionally includesensors capable of detecting linear acceleration in the X, Y, and Zdirections. Embedded computer system 92 includes the aforementionedembedded processor and related circuitry. Motor amplifier 32 amplifiessignals from embedded computer system 92 to drive electric motor 34.Gear reduction 36 is provided, between electric motor 34 and main drivewheel 31 to deliver optimal rotational speed and force.

Ability to Travel in Three Distinct Modes

From the preceding descriptions, the reader will understand that thereconfigurable robot is able to travel in three distinct configurations.These are: (1) A low center of mass four-wheel configuration (“Low 4”),(2) An “A-Frame” four-wheel configuration (“A-Frame 4”), and (3) A highcenter of mass two-wheel configuration (“High 2”). In all threeconfigurations the robot is able to move by providing torque to the rearwheels. In other words, in all three configurations the robot is able tomove as a wheeled vehicle.

Each of the three configurations has advantages. In the Low 4configuration, the overall center of mass is quite low and the robottravels much like a 4-wheel car. It is able to turn rapidly withouttipping. It is also quite resistant to external tipping forces. Thesewill generally cause the vehicle to slide rather than tip over.

The A-Frame 4 configuration allows the robot to raise its payload (suchas a camera or weapon) to a much greater height, thereby affordingenhanced visibility. The ground space occupied by the four wheels isalso reduced in comparison to the Low 4 configuration. The robot maystill be maneuvered as a 4-wheeled vehicle, but care must be taken toavoid tipping. External forces are of course more able to tip the robotas well

The High 2 configuration provides the greatest payload height. It alsoprovides the greatest maneuverability, since the robot can torn in placeby applying differential torque to the rear wheels. However, the robotis more vulnerable to external tipping forces.

As explained previously, the shoulder joints are generally powered whentransitioning between the configurations. However, it is also possibleto lock the shoulder joints in position—preferably using a mechanicalbrake or latch in order to minimize power consumption. For example, itis preferable to lock the shoulder joints when the robot is in the Low 4configuration and the A-Frame 4 configuration. The shoulders may also belocked in the High 2 configuration, though they may also be allowed tomove in order to use the arms for balance and to raise the arms totransition over obstacles, etc.

Some definitions may benefit the reader's understanding. First, therobot should he distinguished from the payload it carries. FIG. 3provides a good illustration of this concept. The robot consistsprimarily of base 20, rear wheels 31, shoulder joints 41, aims 50, 51,and front wheels 60, 61. The robot may include addition features such astrack system 80. The payload in the example of FIG. 3 includes turret 90and camera system 110. FIG. 4 shows the same robot with a differentpayload consisting of turret 90 and weapon system 100.

The robot with no additional payload has a center of mass. This isreferred to as a “robot center of mass.” The rear wheels of the robot(main drive wheels 30, 31) have a rear wheel diameter. When the robot isin the Low 4 configuration, the robot center of mass should be less than100% of the rear wheel diameter of the ground. In other words, in theLow 4 configuration, the robot center of mass should be below the top ofthe rear wheel. This configuration is shown, for example, in FIG. 9(A).

When the robot transitions to the A-Frame 4 configuration, the robotcenter of mass is raised. In this configuration, the robot center ofmass is preferably more than 75% of the rear wheel diameter off thepound, but less than 150% of the rear wheel diameter off the ground.FIGS. 9(E) and (F) provide examples of this configuration—though notnecessarily examples of the extremes of the defined range.

When the robot transitions to the High 2 configuration, the robot centerof mass must of course be higher than 50% of the rear wheel diameter, Asa practical matter, the robot center of mass should be greater than 100%of the rear wheel diameter so that the inverted pendulum balancingtechnique may be used.

In the Low 4 configuration, torque may be applied to the rear wheels andthe front wheels to drive the robot along. In the A-Frame 4configuration, torque may also be applied to all four wheels to drivethe vehicle along. In the High 2 configuration, only the rear wheelstouch the ground. Thus, only the rear wheels apply driving torque.

The robot is designed to roll move efficiently in all threeconfigurations. This efficiency is obtained through the use of poweredwheels. Each configuration has advantages and disadvantages. Eachconfiguration may be the best choice in a particular scenario.

The preceding description contains significant detail regarding thenovel aspects of the present invention. It should not be construed,however, as limiting the scope of the invention but rather as providingillustrations of the preferred embodiments of the invention. As anexample, the reconfigurable may have more utilize multiple joints toprovide greater range of articulation. Such, variations do not alter thefunction of the invention. Thus, the scope of the invention should befixed by the following claims, rather than by the examples given.

Having described our invention, we claim:
 1. A method for adapting areconfigurable robot to travel over varying conditions in the pound overwhich said robot travels, comprising: a. providing a reconfigurablerobot, said reconfigurable robot including, i. a base, having a firstend, a second end, and a forward facing side, with a first rear wheeland a second rear wheel being attached to said first end of said base,ii. said first and second rear wheel having a rear wheel diameter, iii.an arm, having a first end and a second end, with a front wheel beingattached to said second end of said arm, iv. a rotating shoulder jointconnecting said first end of said arm to said second end of said base,v. a track system mounted on said forward facing side of side base; b.said reconfigurable robot having a robot center of mass; c. saidreconfigurable robot being configurable into, i. a low center of massfour-wheel configuration in which said rear wheels and said front wheelrest on said ground and said robot center of mass is less than 100% ofsaid rear wheel diameter off said ground, ii. an A-Frame four-wheelconfiguration in which said rear wheels and said front wheel rest onsaid ground and said robot center of mass is more than 75% but less than150% of said rear wheel diameter off said ground, iii. a high center ofmass two-wheel configuration in which only said rear wheels rest on saidground and said robot center of mass is greater than 100% of said rearwheel diameter off said ground; d. wherein said reconfigurable robot canmove forward by applying torque to said rear wheels in said low centerof mass four-wheel configuration, said A-Frame four-wheel configuration,and said high center of mass two wheel configuration; e. providing saidreconfigurable robot in said low center of mass four-wheelconfiguration; f. applying torque to said shoulder joint to raise saidreconfigurable robot to said A-Frame four-wheel configuration; and g.applying sufficient forward torque to said rear wheels to raise saidfront wheel off said ground and thereafter transition saidreconfigurable robot to said high center of mass two-wheelconfiguration.
 2. The method for adapting a reconfigurable robot asrecited in claim 1, wherein: a. said shoulder joint is lockable; and b.said shoulder joint is locked when said reconfigurable robot is in saidlow center of mass four-wheel configuration and said A-Frame four-wheelconfiguration.
 3. The method for adapting a reconfigurable robot asrecited in claim 2, wherein said shoulder joint is unlocked when saidreconfigurable robot is transitioning from one configuration to another.4. The method for adapting a reconfigurable robot as recited in claim 1,further comprising: a. wherein said Shoulder joint is powered; b.providing a control system for controlling the amount of torque appliedto said front wheel, said rear wheels, and said powered shoulder joint;c. providing an angle sensor for sensing the angle between said base andsaid ground, said angle sensor providing a value for said angle to saidcontrol system; and d. said control system using said value for saidangle to control said applied torques in order to achieve said highcenter of mass two-wheel configuration.
 5. The method for adapting areconfigurable robot as recited in claim 4, further comprising providinga second angle sensor for sensing the angle between said arm and saidbase, said second angle sensor providing a value for said angle betweensaid arm and said base to said control system.
 6. The method foradapting a reconfigurable robot as recited in claim 4, wherein torquesapplied to said front wheel, said rear wheels, and said shoulder jointare applied simultaneously.
 7. The method for adapting a reconfigurablerobot as recited in claim 1, wherein said first rear wheel and saidsecond rear wheel can be driven at different speeds in order to steersaid reconfigurable robot.